In a broad range of fields including, for example, semiconductor integrated circuits such as LSIs, the production of a display surface of FPDs, and the manufacture of circuit boards such as thermal heads, photolithography has hitherto been used for the formation of fine elements or microfabrication. In the photolithography, a photoresist coating liquid, which is a positive-working or negative-working photosensitive resin composition, is used for resist pattern formation.
FIG. 1 shows a conventional coating liquid supplying apparatus used in a conventional manufacturing process using photolithography. In the conventional coating liquid supplying apparatus, in supplying a coating liquid, the coating liquid is generally filled into a supplying vessel 101, for example, a glass vessel, a plastic vessel, a stainless steel vessel, or a drum. This vessel is connected to a pipe 102, and the coating liquid contained in the supplying vessel is supplied to a buffer vessel 104, for example, with a pump 103 or by blowing nitrogen gas or the like into the supplying vessel for pressurization. The coating liquid temporarily supplied to the buffer vessel 104 is if necessary filtered through a filter 105 to remove particles and the like contained in the coating liquid and is then coated through a coating liquid supplying nozzle 108 onto a substrate 106, for example, by a spin coating apparatus 107 shown in FIG. 1. Here a stainless steel vessel having an inner bag as described, for example, in patent document 1 may also be used as the supplying vessel 101. This vessel is as shown in FIG. 2 and has a double structure of an outer vessel 201 made of, for example, stainless steel and an inner bag 202 made of, for example, plastic. For example, nitrogen gas is blown through a gas introduction tube 203 into between the outer vessel 201 and the inner bag 202 to push out and supply a coating liquid contained in the inner bag into a coating apparatus.
On the other hand, the adoption of microfabrication of electronic components in recent years has led to a demand, in the field of the manufacture of electronic components such as semiconductor elements and liquid crystal display elements, that, in supplying and coating a coating liquid onto a substrate such as a silicon wafer, the coating liquid, from which fine particles and the like have been removed, could be efficiently and stably supplied.
Since, however, the coating liquid is supplied from various vessels to the apparatus buffer vessel, for example, the incorporation of foreign matter in pipes or other welded parts and a change in quality (the occurrence or increase of particles) of the coating liquid by physical stress can take place. In this case, when the condition of the coating liquid within the supplying vessel is compared with the condition of the coating liquid within the apparatus buffer vessel, there is a high tendency toward an increase in particles. Further, when a large-capacity supplying apparatus is used in order to lower the frequency of replacement of the supplying vessel, or when a large-capacity buffer vessel is used, for example, from the viewpoint of stabilizing the production process, the residence time of the coating liquid in each vessel is increased, often leading to increased particles with the elapse of time. The particles generated by such causes lead to a failure in the photolithographic process which is causative of a lowered yield of the product.
Accordingly, at the present time, it is common practice to filter the coating liquid through a filter before the supply of the coating liquid onto a substrate (see patent document 2). When the above quality change occurs with the elapse of time, however, single filtration is unsatisfactory for contemplated results and, thus, at the present time, an improvement in yield of electronic components is desired.
In the manufacture of semiconductor elements, in general, spin coating has hitherto been adopted for coating of the coating liquid. According to this method, in the spin coating, most of particles contained in the coating liquid, together with the coating liquid, is spun out to the outside of the substrate, and, thus, the problem of particles could have been considerably alleviated. In high-precision semiconductor elements demanded in recent years, very small quantity or fine particles, which have not hitherto caused any problem, sometimes become a problem. Accordingly, there is a demand for an improvement in quality over the conventional products. Further, wasteful use of the coating liquid by spin coating causes a problem of cost. Therefore, the development of a coating method alternative to the spin coating and an apparatus for supplying a coating liquid having quality high enough to be used in the coating method has been desired.
Patent document 1: Japanese Patent Laid-Open No. 247449/1994
Patent document 2: Japanese Patent Laid-Open No. 24775/1996 (pages 1 to 4)